(a) Field of the Invention
The present invention relates to a pulse width modulation decoder and a cooling device controller.
In particular, the present invention relates to a circuit for controlling a cooling device with a predetermined temperature appropriate for a system.
(b) Description of the Related Art
As personal computer systems have developed to have higher clock rates, clock frequencies for the systems have also increased and the systems' heat generation has become an important issue. As the clock frequency becomes higher, ICs such as a CPU and a memory generate much heat and they may be abnormally operated or be burned without suitable cooling.
Many systems use a cooling fan, which cools the system by circulating the air. The fan sends the system'heated air outside and supplies cold air in its place.
However, the cooling fan generates noise because of the turbulent air flow and the friction of the bearings. If the cooling fan is operated at fixed revolutions per minute (rpm), then for extended intervals it provides more cooling than necessary, accompanied by excess noise. Hence, many systems control the operational rpm of the cooling fan according to the temperature. Some of these systems use thermistors to reduce costs.
A thermistor changes its electrical resistance according to temperature. Accordingly, thermistors are classified as NTC thermistors (Negative Temperature Coefficient Thermistors) whose electrical resistance decreases as the temperature increases, and PTC thermistors (Positive Temperature Coefficient Thermistors) whose electrical resistance increases as the temperature increases.
Even when the temperature is sensed by using a thermistor and the rpm of the cooling fan is controlled accordingly, it is not easy to appropriately control the rpm of the cooling fan because of the nonlinear dependence of the thermistor'resistance on the temperature and the nonlinearly of temperature sensing caused by the thermistor peripheral circuits. Most of the systems control the rpm of the cooling fan to be greater than necessary, thus consuming excessive power and generating excessive noise.